High-durability superlattice wurtzite ferroelectric material, preparation method therefor, and use thereof

Abstract

Disclosed in the present invention are a high-durability superlattice wurtzite ferroelectric material, a preparation method therefor, and a use thereof. The high-durability superlattice wurtzite ferroelectric material is a stacked structure composed of wurtzite ferroelectric thin films and AlN thin films arranged alternately. The total number of layers in the stacked structure is more than 2, and the first layer and the last layer in the stacked structure are both wurtzite ferroelectric thin films. The preparation method comprises: depositing a layer of wurtzite ferroelectric thin film on a substrate; depositing a layer of AlN thin film on the obtained wurtzite ferroelectric thin film; depositing a layer of wurtzite ferroelectric thin film on the obtained AlN thin film; and repeating these operations until a desired stacked structure is formed, wherein the material can be used in a ferroelectric memory. By means of the insertion of the AlN thin films having good lattice matching performance between the wurtzite ferroelectric thin films, the present invention shows improved durability of the thin films, so that the superlattice structure exhibits excellent properties such as low defects, low leakage current, and high durability, thereby improving the breakdown resistance and durability of a ferroelectric memory when applied to the ferroelectric memory.

Description

A Highly Durable Superlattice Wurtzite Ferroelectric Material, Its Preparation and Application Technical Field

[0001] This invention belongs to the field of memory technology, and specifically relates to a high-durability superlattice wurtzite ferroelectric material and its preparation and application. Background Technology

[0002] Wurtzite ferroelectric memory (WFEM) is a potential candidate for in-memory non-volatile memory due to its large storage window, multi-level storage capability, and low thermal budget. However, WFEM currently faces the problem of low durability, typically limited to about 10... 5 ~10 7 The read / write operation cycle is only a few cycles, which is far below the level required for large-scale commercial applications. At the same time, its breakdown characteristics and leakage current characteristics also need to be further improved. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a high-durability superlattice wurtzite ferroelectric material and its preparation and application, so as to solve the problems of low durability and high leakage current of wurtzite ferroelectric memory.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, the present invention provides a high-durability superlattice wurtzite ferroelectric material, wherein the high-durability superlattice wurtzite ferroelectric material is a stacked structure composed of alternating wurtzite ferroelectric thin films and AlN thin films, wherein the total number of layers in the stacked structure is greater than 2, and the first and last layers of the stacked structure are both wurtzite ferroelectric thin films.

[0006] In one embodiment, the material of the wurtzite ferroelectric thin film is AlScN ferroelectric material, AlBN ferroelectric material, or gallium nitride-based ferroelectric material. For example, the gallium nitride-based ferroelectric material can be GaScN ferroelectric material or GaYN ferroelectric material, etc.

[0007] In one embodiment, the thickness of each wurtzite ferroelectric thin film ranges from 5 nm to 30 nm; the thickness of each AlN thin film ranges from 5 nm to 20 nm.

[0008] In one embodiment, the total thickness of the high-durability superlattice wurtzite ferroelectric material ranges from 40 nm to 500 nm, within which the thickness and number of wurtzite ferroelectric thin film layers and the thickness and number of AlN thin film layers are selected.

[0009] A second aspect of the present invention provides a method for preparing a high-durability superlattice wurtzite ferroelectric material as described in the first aspect, comprising the following steps:

[0010] Step 1: Deposit a wurtzite ferroelectric thin film on the substrate;

[0011] Step 2: Deposit an AlN film on the wurtzite ferroelectric film obtained in the previous step;

[0012] Step 3: Deposit a wurtzite ferroelectric thin film on the AlN film obtained in the previous step;

[0013] Step 4: Repeat steps 2 and 3 until the desired stacking structure is formed.

[0014] A third aspect of the present invention provides the application of the high-durability superlattice wurtzite ferroelectric material described in the first aspect in ferroelectric memory.

[0015] In one embodiment, the ferroelectric memory includes the stacked structure, and a bottom electrode and a top electrode respectively disposed on both sides of the stacked structure.

[0016] In one embodiment, the ferroelectric memory can be prepared by the following process:

[0017] Step 1: Deposit and fabricate the bottom electrode on the substrate;

[0018] Step 2: Deposit a wurtzite ferroelectric thin film on the bottom electrode;

[0019] Step 3: Deposit an AlN film on the wurtzite ferroelectric film obtained in the previous step;

[0020] Step 4: Deposit a wurtzite ferroelectric thin film on the AlN film obtained in the previous step;

[0021] Step 5: Repeat steps 3 and 4 until the desired multi-layered stacked structure is formed;

[0022] Step 6: Sputter and deposit the top electrode on the last wurtzite ferroelectric thin film, and perform photolithography and etching to obtain the ferroelectric memory.

[0023] In one embodiment, a ferroelectric memory array is formed by using individual ferroelectric memory units as storage cells. Each storage cell is connected to an external electric field through an independent control line. By adjusting the direction of the external electric field, the polarization direction of the storage cell is controlled, thereby encoding its state as logic "0" or "1". This invention improves the durability of individual storage cells, thereby enabling data storage with ultra-high erase and write cycles.

[0024] Compared with the prior art, the present invention improves the durability of the wurtzite ferroelectric thin film by inserting an AlN thin film with good lattice matching performance into the wurtzite ferroelectric thin film, so that the superlattice structure exhibits excellent properties such as low defects, low leakage current and high durability. In turn, when applied to ferroelectric memory, it improves the breakdown resistance and durability of ferroelectric memory. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the structure of the high-durability superlattice wurtzite ferroelectric material of the present invention.

[0026] Figure 2 is a schematic diagram illustrating the effect of the AlN thin film on grain boundary interruption and vacancy migration in an embodiment of the present invention.

[0027] Figure 3 shows the transmission electron microscope images and energy-dispersive X-ray spectra of the superlattice wurtzite ferroelectric material with high durability in the embodiments of the present invention, as well as the AlScN structure.

[0028] Figure 4 is a schematic diagram of the ferroelectric memory obtained by the present invention using high-durability superlattice wurtzite ferroelectric material.

[0029] Figure 5 is a schematic diagram of the specific fabrication process of a ferroelectric memory in an embodiment of the present invention. Detailed Implementation

[0030] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0031] Referring to Figure 1, this invention relates to a highly durable superlattice wurtzite ferroelectric material, which is a stacked structure composed of at least two layers of wurtzite ferroelectric thin films 1 and at least one layer of AlN thin film 2, wherein the first and last layers of the stacked structure are both wurtzite ferroelectric thin films 1. By inserting the AlN thin film 2, this invention can reduce the possibility of grain boundaries penetrating the ferroelectric thin film, reduce the number of leakage channels, and improve the durability of the wurtzite ferroelectric material.

[0032] Specifically, a superlattice structure refers to a nanoscale structure composed of two or more different materials with well-matched lattices, formed by periodic stacking, with a periodic length typically ranging from several to tens of nanometers. A superlattice is a special case of a heterostructure. This invention utilizes wurtzite ferroelectric thin film 1 and AlN thin film 2, which have good lattice matching properties, to form a "superlattice" by alternately growing a periodic structure.

[0033] In traditional thin film deposition processes, dislocations are generated within wurtzite ferroelectric thin films due to lattice mismatch, and these dislocations typically extend throughout the entire film. In this invention, by inserting an AlN thin film 2, the extension path of dislocations throughout the film can be blocked, confining the dislocations within a single layer of wurtzite ferroelectric thin film 1. This reduces the dislocation density in the entire multilayer stacked structure, thereby improving crystal orientation consistency and reducing the overall dislocation density of the thin film.

[0034] Furthermore, during the deposition process, the high temperature can cause the interface oxide layer and nitrogen vacancies formed in the non-in-situ preparation to diffuse along the grain boundaries, resulting in an uneven distribution of defect concentration in the film. In durability testing, the application of a high electric field and electrical stress can lead to the formation of leakage channels, causing excessive Joule heating and ultimately hard breakdown of the film. This invention addresses this by stacking a wurtzite ferroelectric film 1 and an AlN film 2 to form a periodic superlattice structure. This structure limits the range of leakage channels caused by defects. Simultaneously, through crystal plane torsion and grain boundary interruption, it improves the durability of the film, enabling the superlattice structure to exhibit excellent properties such as low defects, low leakage current, and high durability.

[0035] In embodiments of the present invention, the material of the wurtzite ferroelectric thin film 1 can be AlScN ferroelectric material, AlBN ferroelectric material, gallium nitride-based ferroelectric material, etc., all of which have good lattice matching performance with AlN. For example, the gallium nitride-based ferroelectric material can specifically be GaScN ferroelectric material or GaYN ferroelectric material, etc. It is known that various ferroelectric materials have certain component ratio requirements. For example, for AlScN ferroelectric material, based on the total molar amount of Al and Sc, a Sc content of 0.1-0.4% exhibits relatively obvious ferroelectricity. Since this component content is an inherent value of the ferroelectric material, the component content range will not be described in this invention.

[0036] In embodiments of the present invention, assuming the number of AlN thin film 2 is K, the number of wurtzite ferroelectric thin film 1 is K+1. K is limited by the precision of the thin film magnetron sputtering equipment and the overall thickness required for film miniaturization. A thinner AlN thin film 2 helps form more interfaces, thereby increasing the interface barrier density and enhancing the ability to confine defects. An excessively thick AlN thin film 2 may reduce the total polarization intensity of the superlattice; therefore, the thickness of the intercalation layer, i.e., the AlN thin film 2, needs to be reasonably controlled. Under the premise of controlling the total material thickness, increasing the number of AlN thin film 2 layers not only significantly increases the number of interfaces in the superlattice but also further optimizes the ferroelectric properties of the material. Specifically, more AlN thin film 2 introduces additional interfaces, which help to significantly increase the ratio of breakdown field strength to coercive field, thereby enhancing the film material's resistance to electrical breakdown. Furthermore, the interface effect can effectively suppress the migration of nitrogen vacancies and suppress leakage current generation, thereby improving the durability characteristics of the film.

[0037] For example, the total thickness of the high-durability superlattice wurtzite ferroelectric material ranges from 40 nm to 500 nm, designed to maintain excellent ferroelectric properties and long-term structural stability at miniaturized dimensions. This embodiment uses 190 nm, a moderate thickness that ensures reliability and fabrication compatibility in memory applications. In the structure shown in Figure 1, taking K=5 and AlScN as the material for wurtzite ferroelectric film 1, this invention aims to enhance the reliability of the wurtzite ferroelectric film by increasing the number of interfaces and reducing the propagation rate of deflection dendrites. On one hand, AlN film 2 and AlScN film have good lattice matching characteristics. On the other hand, since crystal plane torsion and grain boundary interruption have a significant effect on the migration of nitrogen vacancies and the suppression of leakage current, they significantly reduce leakage current and increase the ratio of breakdown electric field strength to coercive electric field. Ultimately, the durability of the superlattice wurtzite ferroelectric material can be improved by up to four orders of magnitude, reaching 10. 9 One read / write operation cycle.

[0038] Meanwhile, AlN film 2, acting as an insertion layer, can influence defect modulation and interfacial barriers, and suppress nitrogen vacancy migration. Specifically, referring to Figure 2, nitrogen vacancies are common point defects in wurtzite structures, significantly affecting leakage current, dielectric loss, breakdown field strength, and durability. Because the Al-N bonds in AlN film 2 are more stable than those in AlScN, the formation energy of nitrogen vacancies in AlN film 2 is higher, reducing nitrogen vacancy formation and migration. The introduction of AlN film 2 disrupts the grain boundary continuity of AlScN, significantly increasing the migration barrier and thus reducing nitrogen vacancy mobility.

[0039] In embodiments of the present invention, the thickness of each wurtzite ferroelectric thin film 1 ranges from 5 nm to 30 nm. Within this thickness range, a good balance is achieved between the excellent ferroelectric properties of the wurtzite ferroelectric thin film and the requirement for miniaturization. The thickness of each wurtzite ferroelectric thin film 1 is further preferably 25 nm. A 25 nm thick wurtzite ferroelectric thin film provides sufficient and stable ferroelectric polarization while maintaining moderate interface control capability. A 25 nm thickness reduces stress concentration within the superlattice and forms a good lattice match with the AlN thin film 2. Furthermore, magnetron sputtering or molecular epitaxy equipment can precisely control the 25 nm thickness, avoiding lattice defects caused by excessive thinness.

[0040] In embodiments of the present invention, the thickness of each AlN thin film 2 ranges from 5 nm to 20 nm. Within this thickness range, the interface barrier formed is moderate, which can suppress leakage current without significantly reducing the overall polarization performance. Furthermore, AlN thin films 2 within this thickness range can balance film uniformity and lattice stability, reducing stress concentration within the structure. The thickness of each AlN thin film 2 is further preferably 8 nm. An 8 nm thickness can more effectively increase the formation energy and migration barrier of nitrogen vacancies, significantly reducing defect concentration. Simultaneously, an 8 nm thickness is easily controlled in magnetron sputtering or molecular beam epitaxy equipment and can maintain the periodicity and uniformity of the superlattice structure.

[0041] The high-durability superlattice wurtzite ferroelectric material of the present invention can be prepared by the following steps:

[0042] Step 1: Deposit a wurtzite ferroelectric thin film 1 on the substrate; the substrate used in this invention includes, but is not limited to, heavily doped Si, Pt, TiN, W, Mo, sapphire, Ge and other metal or semiconductor substrates.

[0043] Step 2: Deposit an AlN film 2 on the wurtzite ferroelectric film 1 obtained in the previous step.

[0044] Step 3: Deposit a wurtzite ferroelectric thin film 1 on the AlN thin film 2 obtained in the previous step.

[0045] Step 4: Repeat steps 2 and 3, and alternately deposit wurtzite ferroelectric thin film 1 and AlN thin film 2 with good lattice matching in situ until the desired multilayer stacked structure is formed.

[0046] Figure 3 shows the HR-TEM and EDS results for AlScN and superlattice (SL) structures. HR-TEM analysis clearly shows that the grain size in the SL structure is significantly larger than that in AlScN, while the grains in AlScN are smaller and have denser grain boundaries. This high density of grain boundaries increases the number of leakage channels, leading to more significant leakage. In contrast, the SL structure exhibits superior electrical properties due to its larger grain size and fewer potential leakage channels. Furthermore, the EDS results further verify the successful formation of the AlScN / AlN superlattice stacked structure, demonstrating the effectiveness of precise structural control during the fabrication process. The results shown in Figures 2 and 3 are based on Al... 0.8 Sc 0.2 The principle is the same and the results are similar for AlScN ferroelectric materials with other component contents, since they have the same ferroelectricity.

[0047] Using the high-durability superlattice wurtzite ferroelectric material of the present invention, a typical ferroelectric memory can be obtained, namely, a top electrode 3 is arranged on the top of the superlattice wurtzite ferroelectric material stacked structure, and a bottom electrode 4 is arranged on the bottom of the superlattice wurtzite ferroelectric material stacked structure, as shown in Figure 4.

[0048] This ferroelectric memory can be prepared through the following steps:

[0049] Step 1: Deposit and fabricate the bottom electrode 4 on the substrate. The substrates used in this invention include, but are not limited to, metal or semiconductor substrates such as Si, Pt, TiN, W, Mo, sapphire, and Ge.

[0050] Step 2: Deposit a wurtzite ferroelectric thin film 1 on the bottom electrode 4.

[0051] Step 3: Deposit an AlN film 2 on the wurtzite ferroelectric film 1 obtained in the previous step.

[0052] Step 4: Deposit a wurtzite ferroelectric thin film 1 on the AlN thin film 2 obtained in the previous step.

[0053] Step 5: Repeat steps 3 and 4 until the desired multi-layered stacked structure is formed.

[0054] Step 6: Sputter-deposit the top electrode 3 on the last wurtzite ferroelectric thin film 1, and pattern the top electrode 3 by photolithography and etching to obtain the ferroelectric memory.

[0055] Taking AlScN as the material of the wurtzite ferroelectric thin film 1 as an example, Figure 5 shows its specific preparation process, which is based on sputtering. First, a semiconductor substrate is selected, and surface impurities are removed by ultrasonic cleaning with acetone for 5 min and isopropanol for 5 min. Then, the substrate surface oxide is removed by immersion in DHF solution for 1 min. Next, the bottom electrode 4 is prepared by depositing the bottom metal on the semiconductor substrate. Then, a stacked structure is grown on the bottom electrode 4 using sputter or ALD processes. For the sputter process, the growth of wurtzite AlScN / AlN superlattice thin film material is carried out by alternately depositing AlScN and AlN thin films in a high-temperature, high-nitrogen environment of 200~400 °C while maintaining a high vacuum in the equipment. Specifically, the process utilizes Al-Sc alloy targets or co-sputtering of Al and Sc targets. The film composition is adjusted by modifying the target sputtering power and the nitrogen / argon mixed gas. During AlScN film deposition, every 5-30 nm of AlScN film is followed by a 5-20 nm thick AlN film deposited using an Al target to control grain boundaries and reduce defect state density. For the ALD process, under high vacuum conditions, at a high temperature of 300-450 °C, suitable Sc and Al precursors are selected, and ammonia is used as the nitrogen source to alternately deposit AlScN and AlN films. Finally, a top electrode 3 is fabricated by sputtering Pt or TiN metal electrodes, and the final wurtzite ferroelectric memory is prepared using photolithography and etching.

[0056] In summary, the superlattice structure of this invention significantly reduces defect generation and migration, decreases leakage current in non-volatile ferroelectric memories, and enhances the breakdown electric field strength, thereby significantly improving the device's high durability, especially its performance during repeated erase and write operations, ensuring long-term high-performance stability. Ultimately, this invention lays a solid foundation for high-durability storage technology and the integrated in-memory computing application of ferroelectric memories.

Claims

1. A high-durability superlattice wurtzite ferroelectric material, characterized in that, The high-durability superlattice wurtzite ferroelectric material is a stacked structure composed of alternating wurtzite ferroelectric thin films and AlN thin films. The total number of layers in the stacked structure is greater than 2, and the first and last layers of the stacked structure are both wurtzite ferroelectric thin films.

2. The high-durability superlattice wurtzite ferroelectric material according to claim 1, characterized in that, The material of the wurtzite ferroelectric thin film is AlScN ferroelectric material, AlBN ferroelectric material or gallium nitride-based ferroelectric material.

3. The high-durability superlattice wurtzite ferroelectric material according to claim 2, characterized in that, The gallium nitride-based ferroelectric material is either GaScN ferroelectric material or GaYN ferroelectric material.

4. The high-durability superlattice wurtzite ferroelectric material according to claim 1, characterized in that, The thickness of each wurtzite ferroelectric thin film ranges from 5 nm to 30 nm; the thickness of each AlN thin film ranges from 5 nm to 20 nm.

5. A high-durability superlattice wurtzite ferroelectric material according to claim 1, 2, 3, or 4, characterized in that, The total thickness of the high-durability superlattice wurtzite ferroelectric material ranges from 40 nm to 500 nm.

6. The method for preparing a high-durability superlattice wurtzite ferroelectric material according to claim 1, characterized in that, Includes the following steps: Step 1: Deposit a wurtzite ferroelectric thin film on the substrate; Step 2: Deposit an AlN film on the wurtzite ferroelectric film obtained in the previous step; Step 3: Deposit a wurtzite ferroelectric thin film on the AlN film obtained in the previous step; Step 4: Repeat steps 2 and 3 until the desired stacking structure is formed.

7. The application of the high-durability superlattice wurtzite ferroelectric material of claim 1 in ferroelectric memory.

8. The application according to claim 7, characterized in that, The ferroelectric memory includes the stacked structure, and a bottom electrode and a top electrode respectively disposed on both sides of the stacked structure.

9. The application according to claim 8, characterized in that, The ferroelectric memory is prepared through the following process: Step 1: Deposit and fabricate the bottom electrode on the substrate; Step 2: Deposit a wurtzite ferroelectric thin film on the bottom electrode; Step 3: Deposit an AlN film on the wurtzite ferroelectric film obtained in the previous step; Step 4: Deposit a wurtzite ferroelectric thin film on the AlN film obtained in the previous step; Step 5: Repeat steps 3 and 4 until the desired stacking structure is formed; Step 6: Sputter and deposit the top electrode on the last wurtzite ferroelectric thin film, and perform photolithography and etching to obtain the ferroelectric memory.

10. The application according to claim 8, characterized in that, Ferroelectric memory arrays are composed of individual ferroelectric memory units. Each memory unit is connected to an external electric field through an independent control line. By adjusting the direction of the external electric field, the polarization direction of the memory unit is controlled, thereby encoding its state as logic "0" or "1".

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